Based on our earlier work ("Towards networks with intelligent packets", Proc. 14th Int. Symp. on Computer and Information Sciences, p. 1-11, Oct. 1999), we discuss packet networks in which intelligent capabilities for routing and flow control are concentrated in the packets, rather than in the nodes and protocols. This paper describes a possible testbed to test and evaluate their capabilities, and presents an analytical model for the worst and best case performance of such systems.